In recent years, demand for Gbps-level high speed data communication has been improved for indoor radio apparatuses. In such Gbps-level high speed data communication, usage of high-frequency bands such as 60 GHz bands (i.e., milliwave bands) has been advanced.
Since transmission (reception) amplifiers for high-frequency bands are required to have a small (electric) power amplifying gain and a low power consumption, it is difficult to obtain high output power (i.e., low noise performance). Therefore, insufficient output power is covered using directional gain of an antenna.
For indoor use of a radio apparatus, downsizing of the relevant communication module is required, so that a planar antenna (e.g., patch antenna) is used instead of a three-dimensional antenna (e.g., horn antenna). Generally, planar antennas have a minute open area, and thus it is difficult to obtain a high directional gain by a single element. Therefore, the directional gain is increased using arrayed antennas.
In the arrayed antenna structure, equal-length wiring is generally used for the input from a transmission (reception) amplifier into arrayed antennas. This is because if phase and power with respect to the input into the antenna elements are irregular, the beam emitted from the array antenna is not perpendicular to the relevant antenna plane, which also causes an increase in the level of side lobes.
However, in the high-frequency bands such as milliwave bands, the equal-length wiring may degrade the performance of radio apparatuses as described below. That is, when employing the equal-length wiring, the length of each line should be the same as that of the antenna which is positioned farthest from a signal source. In this case, in order to feed an antenna element close to the signal source, line arrangement for excess length is performed, which requires an extra useless space. In addition, the larger the number of the antenna elements, the harder the arrangement thereof becomes.
Patent Document 1 discloses a technique for omitting the line arrangement for excess length while employing the equal-length wiring. In the disclosed technique, the line arrangement for excess length can be omitted by increasing an effective line length by applying a substrate, that has a high dielectric constant, to wiring parts having a short line length. Patent Documents 2 to 4 are also known as prior art documents relating to array antennas.